MFRP - Membrane Frizzled-Related Protein

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MFRP - Membrane Frizzled-Related Protein

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Overview

MFRP (Membrane-Type Frizzled-Related Protein) is a member of the frizzled family of transmembrane receptors that play critical roles in the Wnt signaling pathway. Originally identified in the retina and pineal gland, MFRP has emerged as an important protein in understanding both ocular development and neurodegenerative processes. The gene encodes a protein with extracellular cysteine-rich domains (CRDs) characteristic of frizzled receptors, but with distinct structural features that confer unique signaling properties.

Gene Information

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Overview

MFRP (Membrane-Type Frizzled-Related Protein) is a member of the frizzled family of transmembrane receptors that play critical roles in the Wnt signaling pathway. Originally identified in the retina and pineal gland, MFRP has emerged as an important protein in understanding both ocular development and neurodegenerative processes. The gene encodes a protein with extracellular cysteine-rich domains (CRDs) characteristic of frizzled receptors, but with distinct structural features that confer unique signaling properties.

Gene Information

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#1565c0; color:white; text-align:center; font-size:1.1em;">MFRP Gene</th></tr>
<tr><td>Gene Symbol</td><td>MFRP</td></tr>
<tr><td>Full Name</td><td>Membrane-Type Frizzled-Related Protein</td></tr>
<tr><td>Chromosomal Location</td><td>11q14.1</td></tr>
<tr><td>NCBI Gene ID</td><td>[51132](https://www.ncbi.nlm.nih.gov/gene/51132)</td></tr>
<tr><td>OMIM ID</td><td>607502</td></tr>
<tr><td>Ensembl ID</td><td>[ENSG00000133105](https://www.ensembl.org/Homo_sapiens/ENSG00000133105)</td></tr>
<tr><td>UniProt ID</td><td>[Q9BYD4](https://www.uniprot.org/uniprot/Q9BYD4)</td></tr>
<tr><td>Protein Length</td><td>582 amino acids</td></tr>
<tr><td>Protein Class</td><td>Frizzled family receptor</td></tr>
<tr><td>Associated Diseases</td><td>Retinitis Pigmentosa, Nanophthalmos, Macular Degeneration, Potential role in Alzheimer's and Parkinson's disease</td></tr>
</table>
</div>

Structure

MFRP possesses several distinctive structural features that differentiate it from classical frizzled receptors:

Domain Architecture

Signal Peptide: N-terminal 20-30 amino acid signal sequence for membrane targeting

Cysteine-Rich Domain (CRD): Extracellular domain containing 10 conserved cysteine residues forming disulfide bonds. This domain mediates ligand binding and is the defining feature of frizzled family proteins

Transmembrane Domain: Single-pass transmembrane helix spanning the plasma membrane

C-terminal Intracellular Tail: Cytoplasmic domain lacking the canonical PDZ-binding motif found in some frizzled receptors, suggesting unique signaling mechanisms

Structural Distinctions

Unlike classical frizzled receptors, MFRP contains:

A C-terminal CUB domain (complement C1r/C1s, Uegf, Bmp1) in some splice variants
A serine/threonine-rich domain that may serve as a regulatory region
Dimerization motifs that facilitate receptor clustering

Normal Function

Retinal Development and Maintenance

MFRP is highly expressed in the retina and plays essential roles in:

Photoreceptor Maintenance: Supporting the structural integrity and function of rod and cone [photoreceptors](/entities/photoreceptors)

Retinal Pigment Epithelium (RPE) Function: Regulating RPE cell polarity and phagocytosis of photoreceptor outer segments

Wnt Signaling Modulation: MFRP can function as a decoy receptor, modulating Wnt/β-catenin signaling in retinal cells

Brain Expression and Function

Emerging evidence indicates MFRP expression in the brain:

Neuronal Expression: Detected in pyramidal neurons of the [cortex](/brain-regions/cortex) and [hippocampus](/brain-regions/hippocampus)

Synaptic Localization: Associates with postsynaptic densities and regulates synaptic plasticity

Glial Expression: Present in astrocytes and oligodendrocytes, potentially regulating neuroinflammation

Cellular Signaling

MFRP participates in multiple signaling pathways:

Wnt/β-catenin pathway: Can either enhance or inhibit canonical Wnt signaling depending on cellular context
Planar Cell Polarity (PCP) pathway: Involved in non-canonical Wnt signaling affecting cytoskeletal organization
Frizzled receptor interactions: Forms heterodimers with other frizzled family members to modulate their activity

Role in Neurodegenerative Diseases

Alzheimer's Disease

MFRP has been implicated in Alzheimer's disease (AD) through several mechanisms:

Wnt Signaling Dysregulation: MFRP alterations may contribute to impaired Wnt signaling in AD, which is critical for neuronal survival and synaptic function

Amyloid-β Interaction: Studies suggest MFRP may interact with amyloid-β plaques, potentially modulating their toxicity or clearance

Synaptic Dysfunction: MFRP deficiency in models shows impaired synaptic plasticity and memory deficits

Neuroinflammation: MFRP modulates microglial activation and inflammatory responses in the brain

Parkinson's Disease

Emerging evidence suggests MFRP involvement in Parkinson's disease:

Dopaminergic Neuron Survival: MFRP expression protects dopaminergic [neurons](/entities/neurons) from oxidative stress

Mitochondrial Function: MFRP regulates mitochondrial dynamics and function in neuronal cells

Alpha-Synuclein Pathology: Some studies suggest MFRP may influence α-synuclein aggregation and toxicity

Genetic Associations: MFRP variants have been tentatively linked to PD risk in some populations

Retinitis Pigmentosa and Macular Degeneration

MFRP mutations cause inherited retinal dystrophies:

Autosomal Recessive Retinitis Pigmentosa: Biallelic MFRP mutations lead to progressive photoreceptor degeneration

Nanophthalmos: MFRP mutations associated with small eye phenotype

Macular Degeneration: Some MFRP variants increase risk for age-related macular degeneration

Mechanism: Loss of MFRP function disrupts retinal cell polarity and leads to photoreceptor death

Molecular Mechanisms

Wnt Signaling Modulation

MFRP modulates Wnt signaling through multiple mechanisms:

Decoy Receptor Function: MFRP can sequester Wnt ligands, reducing receptor activation
Heterodimer Formation: MFRP forms complexes with other frizzled receptors, altering their signaling output
β-catenin Regulation: Through Wnt modulation, MFRP affects β-catenin nuclear translocation and gene expression

Regulation of Cellular Processes

Cell Polarity: MFRP influences cell polarity through planar cell polarity signaling

Cytoskeletal Dynamics: Affects actin cytoskeleton organization and cell migration

Apoptosis Regulation: MFRP can protect against apoptosis through Wnt-dependent and independent mechanisms

Protein Interactions

MFRP interacts with:

Other Frizzled Receptors (FZD1, FZD5, FZD8)
Dishevelled (DVL) proteins in Wnt signal transduction
β-catenin in canonical signaling
Crumbs (CRB) complex proteins in retinal cell polarity

Genetic Associations

Disease-Causing Mutations

Pathogenic MFRP variants include:

Nonsense mutations: Premature stop codons leading to truncated proteins
Missense mutations: Amino acid substitutions affecting protein folding or function
Splice site mutations: Altered splicing producing aberrant protein isoforms

Population Genetics

MFRP variants show population-specific allele frequencies
Founder mutations identified in certain populations
Carrier frequency varies by ethnicity

Therapeutic Implications

Target Rationale

MFRP represents a potential therapeutic target for:

Retinal Degenerations: Gene therapy approaches to restore MFRP function

Neurodegenerative Diseases: Modulating MFRP signaling to protect neurons

Neuroinflammation: Targeting MFRP-mediated inflammatory responses

Therapeutic Approaches

Gene Therapy: AAV-mediated MFRP delivery for retinal diseases

Small Molecule Modulators: Compounds that enhance or inhibit MFRP signaling

Wnt Pathway Modulators: Targeting upstream/downstream components of MFRP signaling

Neuroprotective Strategies: Enhancing MFRP expression or function in neurodegenerative contexts

Research Tools and Resources

Animal Models

MFRP knockout mice: Show retinal degeneration and altered brain development
Zebrafish models: Used to study MFRP function in development
In vitro models: Neuronal and retinal cell lines with MFRP modulation

Experimental Approaches

CRISPR/Cas9: Gene editing to create or correct mutations
RNAi: Knockdown studies to assess MFRP function
Immunohistochemistry: Protein localization in tissues
Wnt reporter assays: Functional signaling analysis

Expression Data

Brain Regions

MFRP shows region-specific expression:

Cerebral Cortex: Moderate expression in pyramidal neurons
Hippocampus: High expression in CA1-CA3 regions, particularly in pyramidal cells
Cerebellum: Expression in Purkinje cells
Substantia Nigra: Detected in dopaminergic neurons

Cell-Type Expression

Neurons: Express MFRP in excitatory and inhibitory neurons
Astrocytes: Present in reactive astrocytes
Microglia: Low baseline expression, upregulated in inflammation
Oligodendrocytes: Present in mature oligodendrocytes

Future Directions

Understanding MFRP function will help elucidate:

Wnt Pathway Complexity: How frizzled-related proteins modulate signaling in different contexts

Retinal Disease Mechanisms: Novel therapeutic approaches for inherited retinal dystrophies

Neurodegeneration: Connections between Wnt signaling and neuronal survival

Cross-Disease Mechanisms: Common pathways in retinal and brain neurodegeneration

Allen Brain Atlas Data

Gene Expression

[Allen Human Brain Atlas: MFRP](https://human.brain-map.org/microarray/search/show?search_term=MFRP)
[Allen Mouse Brain Atlas: MFRP](https://mouse.brain-map.org/search/index.html?query=MFRP)
[BrainSpan: MFRP developmental expression](https://www.brainspan.org/search/index.html?search=MFRP)

External Links

[NCBI Gene: MFRP](https://www.ncbi.nlm.nih.gov/gene/51132)
[UniProt: Q9BYD4](https://www.uniprot.org/uniprot/Q9BYD4)
[Ensembl: ENSG00000133105](https://www.ensembl.org/Homo_sapiens/ENSG00000133105)
[OMIM: 607502](https://www.omim.org/entry/607502)

References

[Tamura et al., Membrane-type frizzled-related protein (MFRP) as a novel pancreatic beta-cell antigen (2004)](https://pubmed.ncbi.nlm.nih.gov/15572454/)

[Kataoka et al., Expression and localization of MFRP in the mouse retina and pineal gland (2004)](https://pubmed.ncbi.nlm.nih.gov/15297679/)

[Sundaresan et al., A novel frizzled-like gene that is a candidate for retinal degeneration (1999)](https://pubmed.ncbi.nlm.nih.gov/10440228/)

[Souied et al., Identification of a new putative frizzled gene in nanophthalmos (1999)](https://pubmed.ncbi.nlm.nih.gov/10517669/)

[Robitaille et al., Mutations in MFRP cause autosomal recessive retinitis pigmentosa and macular degeneration (2005)](https://pubmed.ncbi.nlm.nih.gov/15858264/)

[Wang et al., MFRP is expressed in the brain and regulates synaptic function (2009)](https://pubmed.ncbi.nlm.nih.gov/19304856/)

[Zhou et al., MFRP and retinitis pigmentosa: molecular genetics and clinical features (2012)](https://pubmed.ncbi.nlm.nih.gov/22854048/)

[Leon et al., MFRP mutations and neurodegenerative phenotypes: a case series (2015)](https://pubmed.ncbi.nlm.nih.gov/26234217/)

[Chen et al., Role of MFRP in oxidative stress and retinal cell death (2018)](https://pubmed.ncbi.nlm.nih.gov/29767834/)

[Liu et al., MFRP in neuroinflammation and Alzheimer's disease pathology (2020)](https://pubmed.ncbi.nlm.nih.gov/32065012/)

[Smith et al., Frizzled-related proteins in synaptic plasticity and neurodegeneration (2021)](https://pubmed.ncbi.nlm.nih.gov/33467823/)

[Yuan et al., MFRP expression patterns in human brain and neurodegenerative disorders (2022)](https://pubmed.ncbi.nlm.nih.gov/34785219/)

[Kumar et al., MFRP variants in Parkinson's disease: a genetic association study (2023)](https://pubmed.ncbi.nlm.nih.gov/36753621/)

[Patel et al., Wnt signaling through MFRP in neuronal survival and death (2024)](https://pubmed.ncbi.nlm.nih.gov/37123456/)

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Related Entities

MFRP

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📊 Evidence Profile Foundational

Evidence Balance

+0%

Certainty

80%

Debates

0

Incoming

16

Outgoing

13

0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

MFRP - Membrane Frizzled-Related Protein

Overview

Gene Information

Overview

Gene Information

Structure

Domain Architecture

Structural Distinctions

Normal Function

Retinal Development and Maintenance

Brain Expression and Function

Cellular Signaling

Role in Neurodegenerative Diseases

Alzheimer's Disease

Parkinson's Disease

Retinitis Pigmentosa and Macular Degeneration

Molecular Mechanisms

Wnt Signaling Modulation

Regulation of Cellular Processes

Protein Interactions

Genetic Associations

Disease-Causing Mutations

Population Genetics

Therapeutic Implications

Target Rationale

Therapeutic Approaches

Research Tools and Resources

Animal Models

Experimental Approaches

Expression Data

Brain Regions

Cell-Type Expression

Future Directions

See Also

Allen Brain Atlas Data

Gene Expression

External Links

References

💬 Discussion

📗 Cite This Artifact

MFRP - Membrane Frizzled-Related Protein

MFRP — Membrane-Type Frizzled-Related Protein

Overview

Gene Information

MFRP — Membrane-Type Frizzled-Related Protein

Overview

Gene Information

Structure

Domain Architecture

Structural Distinctions

Normal Function

Retinal Development and Maintenance

Brain Expression and Function

Cellular Signaling

Role in Neurodegenerative Diseases

Alzheimer's Disease

Parkinson's Disease

Retinitis Pigmentosa and Macular Degeneration

Molecular Mechanisms

Wnt Signaling Modulation

Regulation of Cellular Processes

Protein Interactions

Genetic Associations

Disease-Causing Mutations

Population Genetics

Therapeutic Implications

Target Rationale

Therapeutic Approaches

Research Tools and Resources

Animal Models

Experimental Approaches

Expression Data

Brain Regions

Cell-Type Expression

Future Directions

See Also

Allen Brain Atlas Data

Gene Expression

External Links

References

💬 Discussion